Carbonated beverages lose effervescence, and eventually go "flat," after their containers have been opened. For a sparkling wine, such as champagne, a noticeable decrease in quality can take place in a matter of hours.
This phenomenon strongly influences the manner in which sparkling wines are marketed, sold, and consumed. A typical consumer, for example, is unlikely to open a bottle of sparkling wine to have just one glass, knowing that the unused portion will soon go to waste. Indeed, this is why champagne is traditionally regarded as a beverage for special occasions, where waste is of little concern.
Waste is of great concern, however, to restaurants. It is not uncommon for restaurants that serve sparkling wines by the glass to discard several thousand dollars of product per year, and that amount grows with the number and cost of the brands kept available for by-the-glass sales. Consequently, while many restaurants serve an interesting variety of still (i.e., uncarbonated) wines by the glass, relatively few serve more than a single variety of inexpensive sparkling wine by the glass. This partially explains why the level of connoisseurship, and the level of sales, for sparkling wines is lower than for still wines.
There is a significant body of work directed toward the preservation of opened champagne bottles, as well as some persistent myths. One of the most common myths holds that a silver spoon placed handle-first in the neck of an open bottle will maintain the carbonation of the beverage within. This method is completely without foundation. A method with some merit is the commonly used spring-loaded pressure cap. This passive device is designed to hold escaping carbon dioxide gas within the confines of the bottle, until the pressure in the head space (i.e., the enclosed volume above the liquid) is sufficient to prevent further net escape of gas from the beverage. The flaw in this method is that the gas in the head space comes at the expense of dissolved gas in the liquid; hence, the larger the head space, the more volume there is to fill, and the more gas must leave solution. Furthermore, each time the cap is removed, the process starts over again, further depleting the dissolved carbon dioxide in the beverage.
There are several devices available that attempt to preserve sparkling wines, or other carbonated beverages, by repressurizing the opened container. For example, U.S. Pat. No. 4,273,670 to Robinson et al. and U.S. Pat. No. 5,031,785 to Lemme teach an apparatus that forms a seal over the opening of a bottle and repressurizes it by pumping air into the head space. By adding a pressurized gas, these devices appear at first glance to address the shortcoming of the passive cap described above.
However, these devices turn out to be even worse than the passive cap at what they purport to do. First, air contains oxygen gas, which can rapidly oxidize wine, and excessive oxidation will convert wine into vinegar. Second, pressurized air cannot, even in principle, be used to keep carbon dioxide in solution. The reason has to do with the nature of the gas-liquid equilibrium process. A gas will dissolve into a liquid, or evolve out of a liquid, until a characteristic equilibrium concentration of dissolved gas is reached, as determined by the partial pressure of that gas in the head space and the temperature of the liquid. These processes of absorption and evolution occurs simultaneously and independently of one another. At equilibrium, the two processes exactly balance, such that the rate of absorption just equals the rate of evolution, and the concentration of dissolved gas remains constant.
In other words, carbon dioxide pressure in the head space of a beverage does not, and cannot, prevent carbon dioxide from leaving solution, but rather balances the efflux by creating an equal rate of absorption. Pressurized air cannot be substituted in this process. The introduction of pressurized air to the head space of a carbonated beverage will increase the concentration of nitrogen and oxygen in the beverage, but will have no effect whatever on the equilibrium concentration of carbon dioxide. It is true that macroscopic bubbles of carbon dioxide can be suppressed by applying pressure to the surface of the liquid with air or any other gas, or even by some mechanical means. But the suppression of macroscopic bubbles alone merely slows the rate at which equilibrium is reached. The equilibrium concentration for each gas present is still determined solely by the partial pressure of that particular gas in the head space, and carbon dioxide gas will continue to evolve out of solution until equilibrium is reached even if there are no visible bubbles.
A further shortcoming of devices such as those described in Robinson et al. and Lemme is that they provide no safety feature upon an inadvertent rupture of the pressurized container. An unprotected glass bottle at high pressure can be very dangerous, and the danger increases as the level of liquid decreases: the lesser the volume of the beverage, the greater the volume of the head space, and hence the greater the stored energy of the compressed gas in the head space. While a bottle of unopened sparkling wine is fairly safe, a nearly empty repressurized bottle is a significant hazard.
Other systems, such as those disclosed in U.S. Pat. No. 4,691,842 to Foures, U.S. Pat No. 4,706,847 to Sanke et al., U.S. Pat. No. 5,139,179 to Cecil, U.S. Pat. No. 4,982,879 to Corrado et al., U.S. Pat. No. 5,108,081 to McCann, and U.S. Pat. No. 3,976,221 to Martin et al. teach adding low pressure gases to an open container with a beverage therein, such that the beverage is forced out of the container through a dispenser device. Foures in particular teaches the addition of low-pressure nitrogen to preserve and dispense uncarbonated wines from the original container. However, such devices will not work for highly carbonated beverages like sparkling wines. The reason is that sparkling wines, which are carbonated to about 90 psi, are highly unstable when not held at this elevated pressure. This instability is observable in the vigorous gushing of a carelessly handled bottle of open champagne. Any roughness or debris in the liquid pathway of the dispenser, or any turbulence in the liquid caused by the dispensing process, will cause vigorous foaming. This results in the sparkling wine going flat even as it is being dispensed. Using higher pressures, such as would be required to properly maintain the carbonation of the sparkling wine over time, results in an even more turbulent delivery process, more violent foaming, and an immediate loss of carbonation.
Even if such systems could be made to work for sparkling wines, they would suffer a serious flaw. The established traditions of champagne service call for the presentation of the bottle to the customer, and any device that renders the presentation process difficult, or interferes with the aesthetics of the presentation, is likely to be met with consumer resistance.